Make it separate object, misc or permanent extra, create a simple box for collision, or use some original col model and reshape it to mirror, that would give you all correct settings already. You can look in original models for hierarchy setup

mirrors can be sets as wings lf and rf the reforme the wing COL as the mirror size and about the engine vibrance just detach the engine part and rename it engineblock set the axis to chassis and import sultanrs to get the ID work that's it export your model and test